A lifting cradle of this kind consists primarily of two horizontal beams which each have a vertical extension fixed at one end which is terminated by a holding ring or bar adapted to cooperate with the lifting hook of a loading/unloading arm. The loading body proper is fixed to the vertical extension and to the longitudinal beams which form the cradle (sometimes it is called a skeleton cradle), in practice by bolting or welding.
The correct maneuvering of such a cradle relies on a perfect equivalence between the lifting cradle and the arm with which it is manipulated. This is why standards have been set as to the height of the holding ring or bar relative to the longitudinal beams and the distance by which the ring sits forward relative to the ends of the longitudinal beams. In practice, the forward distance is measured relative to a crossbeam designed, when used for loading the lifting cradle onto a lorry, to come to bear behind the vertical column supporting the bar.
However, these standards, in particular DIN and AFNOR standards, have the disadvantage of requiring different values for the aforementioned distances, so that a lifting cradle conforming to one standard can only be correctly loaded and unloaded by an arm which itself conforms to the same standard. This is disadvantageous because for each loading/unloading operation it is necessary to check the identity of the standards and, if they differ, to arrange to replace either the arm (that is to say in most cases the lorry equipped with the arm) or the lifting cradle.
It has already been proposed, in order to be free of the requirements arising from the difference between the standards, to make the height of the arms adjustable and/or to increase the internal opening of the gripping hook so as to adapt it for lifting cradles conforming to two standards, but this results in decreased safety during manipulations and very rapid wear of the parts in contact.